Structure Definition and 1000 Threads

I plot the tight binding bandstructure of graphene. There is a very good aggrement with ab-inition calculation in the valence band. but there is a problem in the non-localized orbitals of conduction band especially in the Gama(0,0) point. Any suggestion is appreciated.

Hii, I was wondering whether there is any correlation between the energy eigenvalues of a single atom (say He) with the electronic band structure of a collection of He atoms. for example, for He atoms the lowest energy would be the ground state, with 2 electrons. So will the lowest band for a...

Disclaimer: I am a science buff – not a scientist. I am curious to know if there has ever been a theory developed about the infinite nature of the universe, large and small, relating to a fractal structure. I was pondering fractal subdivision, and how it offers at least the theoretical...

Assuming atoms pack together as hard spheres , find the largest intenstihal atom that can fit in a BCC arrangement of iron atoms . Take the radius of the irom atoms as 1,21 Å . Carry out the same calculations for an FCC arrangment of iron atoms . On the basis of these caluclation would you...

I have attached the problem drawing. Please refer to it. This is a lumped mass structure and all elements have the same Modulus of Elasticity and Moment of Inertia. Determine the number of degrees of freedom of the structure So I am thinking between 2 different scenarios. 1 scenario...

Hi all, long time reader first time poster! Just need a hand on this problem I've been stuck on for a few days Homework Statement Let r=(a_1,a_2...a_k) be in S_n. Suppose that ß is in S_n. Show that: ßrß^-1=(ß(a_1), ß(a_2)...ß(a_k)). Homework Equations The Attempt at a...

Dear all, I have been thinking, if insulators have their valence band filled, then which band does the extra electrons go when it is negatively charged?? If it is the conduction band, then it would become a conductor... Similarly, if it is positively charged, there would be a hold in the...

Hi! I'm new here... I'm going to go right to the point. I know that when you take atoms and get them closer together, the discrete energy levels turn into bands. But when I'm facing a band structure plot, such as this one (band structure of aluminum nitride in wurtzite structure)...

If the universe is filled with matter, and that matter causes space-time to bend, wouldn't the over-all structure be closed? Meaning, if I fly off in some random direction I would eventually "wrap around" the universe like a person moving across the surface of a sphere? If so, is this...

Homework Statement [PLAIN]http://broadcastsol.com/123.JPG Prob. 1. The structure of massless members is shown in the figure. Determine the reaction forces at the supports C, and forces in the rod EF and DG. Givens: P, a, b, c. Prob. 2. The structure of massless members is shown...

Hello forum members, I got a nifty new multireference CI program at my hands and now I'm wondering what to do with it. The program is able to correlate general MCSCF wave functions, and as such basically any kind of molecular electronic structure imaginable; in particular also electronic...

Hi I was trying to understand the geometry of Sulphur Dioxide molecule on the basis of hybridisation involved in the central atom. I found that Sulphur atom should have SP2 hybridisation. I want to know that is there any promotion of electron from 3 p-orbitals to 3d-orbitals and then forming...

Is their a method for predicting the molecular shape of molecules without drawing the Lewis structure? I am preparing for an ACS exam and would like to try to save some time on these problems. I think I could determine the steric number by counting the total electrons available, and...

I just studied the structure of the lens of the eye. And I found out that there are two type of fibres present, which were the Circular Fibres and the Radial Fibres. Can anyone please tell me what is the purpose or function of these two fibres ? Or simply they are just fibres which are...

Like, let's say substance A, in the sun, is very hot. After the sun goes down, it stays hot, but after awhile it becomes cold. Element B, in the sun, is also very hot, but after the sun goes out, it basically becomes cold immediately. Why is this?

Hi! I'm new to the physics forum but I've read a little bit and I'm impressed with the knowledge a lot of people have here. I've tried searching for any topic on my question without any luck. My question is simply what the algorithm is to determine the band structure for a one dimensional...

Sorry if someone already posted this link but did anyone see this in the news? http://www.nasa.gov/home/hqnews/2010/nov/HQ_10-295_FERMI.html What are people's opinions on what this might be?

What's the main reason behind the fine structure of X-Ray transition?

A crazed billionaire has a lifelong dream to build the world's tallest structure as a testament to his glory. Fearing competition, he decides that his tower must be far taller than any other in order to remain that way for as long as possible. The goal: build a 10 km tower, and do it in as...

Hi, Could someone help to explain that why for the 2 D system, like 2 dimensional electronic gas, the crystal momentum k in 2D band structure is defined on a torus? Thanks a lot.:)

"A two-dimensional structure is tested in a wind tunnel with an air density of 1 kg/m3. The wind tunnel is 1 m high, with upstream and downstream pressures of 1.5 kPa gage (i.e. above atmospheric) and 1 kPa gage respectively. If the mean velocity of the entering air is 30 m/s and the downstream...

Homework Statement Draw the skeletal structure of the compound with molecular formulaC3H4Cl4 whose proton NMR spectrum contains a down-field triplet and an up-field triplet with relative integration of 2:2. 2. Rationale for Solution Integration ratio of 2:2 means CH2-CH2, after this one carbon...

question about the universe structure? I have a question. Does universe consist curved spacetime everywhere? , I believe there are plenty of flat spacetime, isn't it? . If it is so then eveywhere worm hole is not possible isn't it?

Dear all, I want to calculate the band structure of graphene for a unit cell with 8 atoms in the Tight Binding approximation. There is no problem about drawing the band structure for a unit cell with 2 atoms. But by increasing the unit cell size, first brillouin decrease and there is a gap in...

In the book of the Dr. Ronald Askeland the problem about x-ray diffraction use the next planes indices to calculate the interplanar distance, but I don't understand why to use such planes indices? Are these planes all of planes in a cubic structure? (111) (200) (211)...

Can the density of gas be changed for good, or is the change just temporary? And what increases density in gases?

I just noticed that it's often taken for granted that a macroscopic crystal has a similar geometric structure as in the atomic scale. What is the physical explanation for this (assuming it is true)?

Hello, I'm new here and have joined to ask the following two questions: 1 - The distance to the CMB has been measured at approximately 14 billion light years. How was this achieved, what is the error and is it the same in all directions? 2 - WMAP data clearly shows that the CMB has a plane...

Hi guys, what are some ways to visualize the deflected shape of a simple structure? I know that there is no slope or deflection at fix ends. No deflection at supports (roller, fix ends, etc). Also, I am not really sure what a kink is. Thanks

Has the following explanation for the large scale structure of the universe been considered and discounted?Consider a universe many billions of times the size of the observable universe, so big that the homogeneous nature of the universe could even be an illusion. At a very large distance...

Hello... I was just reading about that, and I have one question. In the chapter I've jut read about, the overall headline is about one electron atoms, so I was just wondering, since the overall equation got Z (Atomic number) in it, if this was for larger atoms as well, or ONLY one electron...

Homework Statement NaCl is a face-centred cubic with a basis at Na(0,0,0) and Cl at (a/2,a/2,a/2) and lattice parameter a = 5.63 angstrom. calculate the separation between nearesr neighbours (Na and Cl). The Attempt at a Solution Just by looking at the NaCl structure the separation...

Hi all, I'm going to ask a naive question - hope that's ok. There's been a lot of recent discussion of the results from Webb et al. which indicate that the fine structure constant varies spatially. I realize the results are very controversial - I'm wondering, hypothetically, if these...

Hello all, I already have the answer to my question, but what I would like to know is why. My question is: why in the question below is the plane 111 used to find ao and not another plane? An ordered compound of NiAl has a cubic structure with one formula unit/cell. One Al atom at...

I am not much of a mathematician, and I am trying to understand Maxwell's equations. I am trying to visualise the structure of a magnetic field produced in a straight wire firstly by a DC current, and secondly by an AC current. I think I understand but I just need to make sure that I have...

Questions concerning GW's are very common on PF, but I think I have a new question on the concept. Maxwell explains that EM waves(photons) propagate in space due to a relationship between the sinusoidal representations of the electric and magnetic fields of the wave. Namely that these...

I guess I don't have much to say about this other than it's pretty amazing if it's true and I wanted to bring it to everyone's attention here. http://www.sciencedaily.com/releases/2010/09/100909004112.htm http://arxiv.org/abs/1008.3907

I understand that it's been determined to have a very small value. At the same time, it is also true that gravity is incredibly weak compared to the other fundamental forces. What I'm wondering whether there might be some relationship between them?

I was wondering if topology has ever been utilized on the structure of DNA and how that applies to its functions? I am assuming that it has as this is one of the most obsessed over molecules in the 21st century. I am interested in this area of topology if it exists. Also I have no previous...

How does one prove that the smooth structure on 2-manifolds is unique? Source? Thx!

The thread "Fine Structure Constant Varies With Direction in Space!" was locked because it didn't cite papers published in refereed journals. Actually all of this stuff has been published in refereed journals. The list of references below is cut and pasted from...

Homework Statement A) Potassium Methoxide, KOCH3 has both covalent & ionic bonds...Which are which? B) Why do you suppose no one has created a stable cyclopentyne molecule? C) How many electrons does a positively charged Carbon atom in a carbocation (C+H3) have? Why is it trigonal...

Here's something profoundly earth-shaking: Thursday, August 26, 2010 http://www.technologyreview.com/blog/arxiv/25673/ A spatial variation in the fine structure constant has profound implications for cosmology -- What is going to have to be revised as a result of this discovery? What are the...

Hi! Hope someone can help, I am currently studying an Open University course and I am a little confused by a statement in one of the textbooks. It says that the value of the fine structure constant increases with collision energy (in Electron/Positron annihilation). I am probably being...

Hi, I have done quite a bit of looking about and I'm aware that there are many forms of penicillin... While looking at the base structure of penicillin i have found two different kinds... At a guess i'd say one is synthetic and one is natural form? Could someone possibly clear this up for...

Hi, Everyone: LetB: E-->X be a line bundle, with scructure group G and X has a CW -decomposition. I am trying to understand why/how, if the structure group G of B is connected, then any trivialization over the 0-skeleton of X can be extended to a trivialization of the...

Hi, Just need to clear up any misunderstanding about protein structure. Do all proteins have at least three levels of structure? If a protein has a quaternary structure, does it mean it also has primary, secondary and tertiary structures? I was wondering what separates a polysaccharide from...

Consider the manifold of the real-line R with a differentiable structure generated by the map x^3 : M \rightarrow \mathbb{R} . This example is given in a textbook I'm looking at, but I don't really understand how this can work. The inverse map is clearly not smooth at x=0. Do they mean that...

I'd like to know how you check that some simple structure's design is adequate. I know that's bound to be a baby question for you engineers but, believe me, the answer isn't easy to get out there in the world for us non-engineers. If I, for instance, draw something like the frame of a...

Please help me in clearing my basic doubt We all know that positive charges are concentrated at the centre of the atom , known as nucleus and electrons revolves around the nucleus in orbits. Is it necessary to assume that orbits are circular ?